Ultra high frequency electric discharge device and cavity resonator apparatus therefor



Aprll 24, 1951 N. r.-L A\voo ET AL 2,550,485

ULTRA HIGH FREQUENCY ELECTRIC DISCHARGE DEVICE AND cAvITY RESONATOR APPARATUS THRREFOR Filed June s, 1949 3'? Antole IV). G grewitsch:

by M ci A Their` Attorney.

Patented Apr. 24, 195

UNITED STATESl PATENT OFFICE ULTRA HIGH FREQUENCY ELECTRIC D IS- CHARGE DEVICE AND' CAVITY v`RESO-'- NATOR APPARATUS THEREFQR,V Y

Our invention relates to space resonant systems for use at ultra high frequencies and more particularly to an ultra high frequency electric discharge device and an associated cavity resonator system adapted to Ibe used with ultra high frequency electromagnetic Waves.'

In ultra high frequency electronic applications, cavity resonator systems are commonly employed in conjunction with a properly constructed electric discharge device Ain order to overcome circuit losses due to the distributed capacity and inductance ofr connecting leads and circuit components. The general size and shape of such electric discharge devices and cavity resonators are' dictated to a great extent by the Awave length of the electromagnetic waves at the frequency to .be employed and the .particular mode ai .which the cavityresonators are to be operated. Where the wave length of the 4electromagnetic wave to be employed is, for example, in the Vicinity '0f 10 centimeters, the size lof these components .must be very small, and dinicultiesfare encountered in arranging them in a proper cooperating relation without sacrificing efficiency orintroducing higher order waves.

As is well known in the art, the greatest eficiencyof such space resonant systems aswell 'as their broadest frequency response "pattern" is accomplished when the cavityrefsonators 'are operated as quarter wave length 'resonant circuits. Because ofthe diminutive' sizeof "cavity resonators operating as quarter wave resonant vcircuits `for centimeter waves, theproblems of construction and component arrangement are'aggravated. Furthermore, since a minute change in the size of such cavity resonators causesa large change in the natural resonant frequency thereof, it becomes exceedingly difficult to construct an efficient quarter wave vspace resonant system which is easily tunable at these ultra high frequencies.

It is `a principal objectof our invention, therefore, to provide an "improved ultra high yfrequency space resonant system. f

Another object of our invention is to provide an improved electric discharge device suitable for use in conjunction with cavity resonators constructed to resonate at ultra high frequencies.

A further object of our invention is to provide an electric discharge device suitable for use in conjunction with cavity resonators Voperating as quarter wave length resonant circuits for electromagneticwaves having a wave length in the 'order of 10 centimeters.

l An additional object of our invention is to provide an improved ultra high frequency space resonant system adapted to vbe used as an amplifier for ultra Yhigh frequency electromagnetic Waves.

A further specific object of our invention is to providejan ultra high frequency cavity resonator system which may be easily tuned over a fairly wideband of frequencies Without a substantial loss of eiiiciency or an-introduction ofghigher order waves. H

One o'f the principal features of our invention is the'provision of an Aelectric discharge device having a small tapered dome of suitable insulating material supportingan anode whose external portion spires axiallyV through the top of the dome. A conductive member which extends out of the base of the dome both supports and enables an' `external connection to a 'grid' of the discharge device. This arrangementy of Velectrodes permits a cylindrical' cavity resonator functioning, for example; as a conventional gridanode output resonating circuit, to be telescoped over this domed end portion of the discharge device. In order to obtain this telescoped arrangement, an 'end' wall of thetresonator lhas a centrally positioned sleeve accommodating and making slidable contact with the externallyextending portion of the anode, while the inner peripheral surface of the cylindrical' Wall of' the resonator is constructed to fit with'close engagement around'the conductive member `at the base of the dome. The natural resonant frequency of this -cavity resonator is controlled by changing the axial'position of the entire resonator with relation to the domed end portion of the electric discharge device.

AThe novel features which we believe to be characteristic 'of our invention are set forth with particularity in the appended claims. The inventionv itself, however, together with further objects and advantages thereof may best be `understood by reference to the following description .takenin connection with the accompanying drawing in which Fig. 1 is a4 sectional View of 'an electric discharge device embodying the invention and Fig. 2 is a sectional view of a space resonant system which'may be employed in conjunction with the electric discharge device of'Fig. 1. Referring to Fig. 1, We have shown an electric discharge'device I embodying our invention having a cathode 2, a first control grid 3, aV second screening grid 4,1 and an anode 5 consecutively spaced along'the axis of the device l. The adjacent end surfaces of the cathode 2 and the anode k5 are in opposed alignment to form electron emitting and electron receiving surfaces. The cathode 2 is heated by a lament within a metallic cylinder 1 which is in conductive relation with the cathode li and extends outside the enclosed region of the discharge device I. One end of the filament 6 is connected to the cathode cylinder 1 while the other end of the filament 6 is connected to a rod 8 which extends axially through the center of cylinder 1 and is supported by a glass sealing disk 3. ,Y Y

Concentrically surrounding the internal portion of cathode cylinder 1 is another conductive cylinder I3 having an inwardly turned shoulder II which functions both to support and make conductive connection to grid 3. The grid cylinder I is maintained in a proper spaced apart relation to the cathode cylinder kl by an Vannular collar I2 of insulating material such as glass which also functions to seal the cylinders 1 and I8 hermetically.

Another annular insulating collar I3 is hermetically sealed at one end to the grid supporting shoulder II'of cylinder I0 and is sealed at the other end to a conductive member or disk It which supports grid l across a centrally located aperture I5 formed in the disk I4. Extending annularly from the circumference of disk It are a plurality of resilient, contact fingers I6. These contact ngers are preferably shaped to overlay insulating collar I3 and to taper outward slightly as illustrated. Although the disk I4 is Apreferably terminated in the contact fingers I8 as illustrated, it will be appreciated that the disk may alternatively be terminated in a solid annular member and that slidable contact to an associated cavity resonator may be accomplished by virtue of contact fingers formed on the resonator.

A tapered insulating member such as the domeshaped member I1, which may also be constructed of glass, extends from the conductive disk I4 at the base of the dome up to a conductive rod I8 which spires axially through the center of the dome. Rod I8 is secured within discharge device l to an anode 5 and forms an externally extending'portion thereof. The domeshaped member I1 functions both to support the anode 5 in a proper spaced relation to grid 4 and to complete the hermetic enclosure of the electrodes of the discharge device I.

The over-all size of the device I is, of course, determined by the Wave length ofthe electromagnetic wave with which it is to be employed. Due to the consecutive spacing of the electrodes 2 to 5, it will be appreciated that a discharge device such as described above may easily be constructed to have very small dimensions without the danger of internal shorting between the electrodes. For operation in the vicinity of l0 centimeters, we have found that an electric discharge device 7 centimeters long having a domeshaped member I1 whose base diameter is 2 centimeters and whose height is 1.25 centimeters is quite satisfactory. ln addition, the step-wise configuration caused by the location of the concentric conductive cylinders 1 and II permits an easy plug-in type of connection to assocated resonant cavities as will be more fully explained hereinafter. Referring to Fig. 2, we have shown the dis- -charge device Yof Fig. l in conjunction with a space resonant system adapted to be employed 'as an amplifier of ultra high frequency voltages.

An inner conductive cylinder 28 and a concentrically positioned outer conductive cylinder 2I define, together with an annular plunger 22, in-

serted intermediate cylinders 20 and 2|, three bounding surfaces of an input cavity resonator 23. The outer cylinder 2I is divided into tWo portions ZI and 2l by an insulating washer 24 placed between two annular conductive flanges 25 and 25 extending radially from adjacent edges of the cylinder portions 2I and 2|" respectively. The flanges 25 and 25 together with the insulating washer 24, which is preferably composed of a suitable dielectric material such as silvered mica, comprise a small capacitor enabling different unidirectionalV potentials to be impressed on each portion of the outer cylinder 2I and also serving as a low `impedance path for high frequency currents between these cylinder portions. A ring 26 of suitable insulating material is interfitted between a turned back portion 25 of flange 25 and the adjacent end of cylinder por-- tion 21'; The entire capacitive assembly is fastened together by such means as screws 28 which secure the ring 26 to the ange portion 2'5.

The inner conductive cylinder 20 terminates in a plurality of resilient contact fingers 21 which are constructed to t contiguously around the outer surface of the external portion of cathode cylinder 1. Similarly, the outer cylinder portion 2|" terminates in a plurality of resilient contact fingers 28 which are constructed to engage the surface of grid cylinder IIJ. The cathode end portion of discharge device I may, therefore, be plugged into the cylinders 20 and 2| thereby completing the enclosure of the input cavity resonator 23 as illustrated. Filament rod 8 thereupon fits Within a socket 29 formed at the end of a conductive rod 30 which extends axially through the center of cylinder 28.

The input space resonant cavity resonator 23, commonly referred toas the grid-cathode space resonant cavity resonator, may be excited in a well-known manner by the inner conductor 3I of a transversely communicating concentric transmission line 32. The natural resonant frequency of this inputcavity resonator 23 may be controlled by adjusting the longitudinal position of the annular plunger 22 with any suitable mechanical means such as a handle 33 and connecting rods 34. The plunger 22 is in close engagement with the surfaces of cylinder 20 and 2l to prevent any discontinuity in the conductive medium which defines the cavity resonator 2'3.

An output cavity resonator 35 is associated with the device I and is dened by another cylindrical member 35 having wheel-like extending portion 31, anda circular conductive end plate 38 which iits against extending portion 31 but is separated ltherefrom by another insulating washer 39 similar to washer 24. The cylinder portion 31, the end plate 38 and the insulating washer 33 also function as a small capacitor to isolate unidirectional potentials applied to the anode 5 and the screening electrode d, while permitting an easy path for ultra high frequency currents-between these components. A cylindrical insulating member dit is sealed at one en d to bothpthe plate 38 and the cylinder portion 31 and thereby serves to secure these components together. Y

Energy may be extracted from this output cavity resonator .35 by any suitable output electrode means such as a coupling loop 4I inserted within the volume of the resonator 35 and making connection between an inner conductor 42 and outer conductor 43 of a coaxial transmission 'asesinas line 44 supported by the wheel-like extending portion 3'I of cylinder36.

` As illustrated in Fig2, end plate 38 is provided 4with a centrally located axially extending sleeve 46 which is constructed to' accommodate the external portion I8`of anode 5. The sleeve 46 terminates in contact fingers 41 which press firmly against the surface Vof the yanode portion I8. Similarly, the contact :lingers Iit'of the grid 'supporting disk I=4 press firmly against the inner peripheral surface of cylindrical conductor 36. Due to the slidable contact made by these fingers I6 and 41', the enclosing portion of the output resonator 35 may be telescoped axiallyY over the domed end portion of the discharge device I. As previously suggested, it is obvious that slidable Icontact between cylindric-al conductor -36 and the external position of gridsupporting disk may alternatively be accomplished by terminating the cylindrical conductor "36 in a plurality of contact fingers instead of the disk I4 as illustrated.

It is evident that this relative longitudinal movement between the output resonator 35 and the discharge device I alters the axial dimension of the output resonator 35 and thereby functions to control its natural resonant frequency. Because of the extremely small length of the electromagnetic Iwaves to be'propagated within this resonator, a minute change in its dimensions causes a relatively large change in its resonant frequency. We, therefore, preferably provide a rotary mechanical driving device whereby the enclosing portion of the resonator 35 may be moved longitudinally in small determinable increments. A tuning knob 48 is threaded on a shaft 49 which is inserted as a free fit through a rigid supportingmember 50. The base of the tuning knob A48 has an annular shoulder 5I which is journalled Within a collar 52 which, in turn, is secured to the supporting member 50. As the knob 4-8 is turned, a longitudinal motion is thereby imparted to the shaft 49. This shaft 49 is secured to a transverse plate 53 which is sealed to the end of cylindrical insulating member 4U. It will be appreciated that insulating member 4o must be long enough to provide considerable spacing between the end of anode portion I and the transverse plate 53 to prevent thearcing'of a high Voltage which may be applied to the anode 5.

A pair of upright mechanically strong insulat- `ving members 54 and i55 support the entire space resonant assembly. The insulating member 55 is securely fastened to the outer surface of cylinder portion 2l iwhile the insulating member 54 has an aperture 56 of slightly larger diameter than the insulating cylinder 40 'which it encircles, thereby to enable the longitudinal motion of shaft 49 to imparta longitudinal movement to the output cavity resonator 35 With respect to the securely positioned discharge device I.

The above-described embodiment of the invention permits proper operating voltages to be easily applied to the various electrodes of the discharge device I. Heating current for the filament 6 may be provided by means of a transformer 51 having one of the terminals of its secondary Winding connected to the outer cylinder portion 2 I land the other terminal connected to rod 36. When used as a voltage Iamplifier, the cathode 2 may be maintained at ground potential by connecting the cylinder portion 2| to ground as indicated in Fig. 2 since the cylinder portion 2| is in electrically conductive relation with the cathode through the plunger 22 and the inner cylinder 20. The proper control grid 3 6 biasing voltage may be provided by such means as a battery 58 having its positive terminal connected to ground and itsnegative terminal connected through a grid return resistance -59 to the cylinder portion 2| A positive voltage may be applied to the screening electrode 4 by a connection 6U to cylindrical conductor 36 of the output resonator 35, `and a proper positive anode voltage may be applied by a connection 60 through a small hole 6I in the insulating cylinder 4|] to the end plate 38 which is in conductive relation with the anode end portion I8.

From the foregoing description, it `will be appreciated thatl the output cavity resonator 35 may be tuned to, resonate at extremely high frequencies with the electrical characteristics of a quarter-wave transmission line short circuited Iat one end and having a capacitive load across its other end. The Vupper limit of frequency to which the resonator may be tunedis, of course, determined byl the position at Iwhich the end plate -38 hits against the top of dome-shaped member I1, while the lower limit of tunable frequency is determined by the point at which the discharge device I no longer makes contact with the walls of resonator 35.

Although we have shown the anode rod portion I8 as having a small diameter relative to the diameter of the outer cylinder 36 in order to provide a resonator which will have a broad band frequency response, it is to be understood that rod I8 as well as anode 5 may have various diameters and cross-sectional configurations in order to provide a resonator having other desired electrical characteristics. It is also to be understood that while we have preferably shown our invention in conjunction with a discharge device having both a screen grid and a control grid, it is equally applicable to a discharge device having only one grid or, on the other hand, having more than two grids. It is necessary only that at least one of the grids employed be provided With an externally Vextending conductive supporting disk such as disk I4 in order to enable the slidable telescoping of a cavity resonator over the output end portion of the discharge device.

It will also be appreciated that by telescoping theV resonator 35 over the domed end of the discharge device I, there is provided a plug-in type of tunable cavity resonator Which has only two regions of slidable contact; one between contact fingers I6 and the inner surface of cylinder 36, and the other between fingers 4l and the anode portion I8. This telescoped arrangement may be contrasted with the conventional type of tunable cavity resonatorl such as the input resonator 23 which has four regions of slidable Contact; one .between fingers 28'and the grid cylinder I I, another between fingers 2l and the cathode cylinder l, and two more regions between the slides of plunger' 22 and the corresponding surfaces of resonator cylinders 20 and 2| respectively. Since the telescoped output resonator 35 has only two regions of slidable contact, the possibility of energy losses due to a discontinuity in the conductive medium defining this resonator 35 are considerably reduced. i

While we have shown a particular embodiment of our invention, it is to be understood that We do not wish to be limited thereto since many modications may be made, and we, therefore, intend by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

1-. Whatiwe claim as; anddesire to; secure by Letters Patent of.' the United nStates is: l

1c Inlanultra highirequency electric discharge device,'a cath.0de, an,anode,-andrat least one grid located intermediate saidcathode and said` anode and in axial alignment therewith, said anode having an axially extending portion, an electrically 'conductive member encircling and connected to said grid, insulating means hermetically sealed between said cathode and said conductive member .to supportY said conductive member in spaced relation to said cathode, and a tapered insulating dome member hermetically sealed at its base to said conductive member and hermetically sealed at its apex to said axial anode portion to support said anode in spaced relation to said grid, said anode portion'having an external portion extending through said apex, said conductive member terminating in a plurality of external contact fingers extending from said base of Said tapered member whereby a grid-anode cavity resonator may be telescoped axially over the anode end portion of said discharge device in contact with said external anode portion and said contact ngers.

2. An ultra high frequency electric discharge device comprising a cathode, a control grid, a screen grid and an anode in consecutive spaced alignment along the axis of said device, said anode having an axially extending conductive rod, said cathode having an axially extending cylindrical portion, a conductive cylinder concentrically surrounding said cathode cylindrical portion, said conductive cylinder being connected to and supporting said controlgrid, la conductive disk connected to and supporting said screen grid and having a plurality of contact fingers extending from the circumference thereof, and insulating means supporting said electrodes in spaced apart alignment including a pair of annular insulating members hermetically sealed respectively between said cathode cylindrical portion and said conductive cylinder, and between said conductive cylinder and said disk, and a substantially dome-shaped insulating member hermetically sealed at its oase to said disk and hermetically sealed at its apex to said rod to complete the enclosure of said electrodes, said rod having a portion extending externally through said apex of said dome, said contact lingers extending externally from said base of said dome.

3. An ultra high frequency cavity resonator system comprising an electric discharge device including a cathode, at least one grid, and an anode in consecutive spaced alignment, a tapered insulating end portion enclosing said grid and said anode, said anode having a portion axially extending externally through the apex of said conical end portion, and a conductive disk in conductive relation with said grid, said disk extending externally from the base of `said tapered end portion; a substantially cylindrical conductor concentrically surrounding said tapered end portion, the inner s uriace of said cylindrical conductor being constructed to slidably engage against said external disk portion, a conductive end plate covering the anode opposing end of said cylindrical conductor and cooperating therewith to deflneagrid-anode cavity resonator, said end plate -having a central sleeve-encircling and making slidable contact with said external portion of said anode, and means to vary the axial position of said resonator relative to said discharge device thereby to tune said resonator.

4. An ultra high frequency space resonant system adapted to be employed with electromagnetic Waves having a Wave length in the order of 10 centimeters comprising anelectric discharge device including a cathode, at least one grid and an anode in consecutive spaced alignment, a substantially dome-shaped insulating end portion enclosing said grid and said anodefsaid anode having a conductive rod portion axially extending externally through the. apex .of said dome, and a-conductive disk encircling and connected to said grid, said disk extending externally from the base of said dome;..a.substantially cylindricall conductor concentrically surrounding said dome-shaped endportion, the. inner surface of said cylindrical conductor being constructed to slidably engage against said external disk portion, a conductive. endplatecovering the anode opposing end..of said cylindrical conductor, said end plate having a ,centralsleeve encircling said anode rod portion and terminating `in a plurality or" resilient contact fingers constructed to press iirmlyagainstsaid rod, said endA plate and said cylindrical conductor ,cooperatingwith said discharge deviceto provide a quarter Wave gridanode resonant cavity,A directcurrent insulating means betweensaid end plate and said cylindrical conductor,A and mechanical means to vary the axial position of said end plate and said cylindrical conductor relative to. said discharge device thereby to tune said resonator.

NORMAN T. LAVOO. ANATOLE M. GUREWITSCH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Bowie Dec. 27, 1949 

